Hollow article and its manufacturing method and apparatus thereof

ABSTRACT

The present invention is a hollow article with an integral impact absorbing rib and the method of manufacturing the same. The apparatus is a hollow article made of thermoplastic resin and integrally formed by blow molding, comprising a first wall and a second wall confronting across a spacing. There is an integral rib between the first wall and the second wall, wherein the integral rib comprises a flat rib between the walls and one or more hollow ribs adjacent to each of two side ends of the flat rib. The impact absorbing rib is disposed at intervals and in an impact action direction. The rib is uniform in shape, dimensions and wall width, and free from reduction of wall width of the inner rib, yet possessing proper structural support and mechanical strength, and excellent in impact absorbing performance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application that is related and claimspriority under 35 U.S.C. §120 to U.S. Non-Provisional application Ser.No. 09/794,579 filed Feb. 27, 2001, now U.S. Pat. No 6,592,358, which isincorporated herein by reference for all purposes, and which in turnclaims priority under 35 U.S.C. Section 119 from a Japanese PatentApplication No. 2000-54898 filed on Feb. 29, 2000, and a Japanese PatentApplication No. 2000-394056 filed on Dec. 26, 2000, which areincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to thermoplastic hollow articles that areexcellent in rigidity and impact absorption qualities, as well as to themanufacturing process for producing the hollow articles.

2. Background Art

Hollow articles are well known in the art and used in a variety ofindustries and applications. These plastic hollow articles arelightweight, strong, and relatively inexpensive to manufacture usinginjection or blow molding techniques.

There are numerous examples of products that employ hollow articles,such as ducts, panels, or housings for electronics, appliances,automobiles, and house wares. In many homes these hollow articles arefound in walls, partitions, and panels, such as entrance doors, andindoor air conditioning ducts. Furniture is also manufactured withhollow structures, and includes top plates of desk, partition panels,and bookshelf panels.

In the appliance sector, housings of some of the components are hollowsuch as used for refrigerators and televisions. The hollow articles arealso used in office equipment, such as the housings of copy machines,facsimile machines and computer peripherals.

Panels and ducts of dwelling facilities, furniture panel, housing ofelectric household appliances, housing of office equipment andautomotive parts are often required to have a high rigidity. Hollowarticles used in such applications are manufactured in integralstructures combining a first wall and a second wall by means of a riblinking them mutually within a hollow space. In cases where theappearance is important on both face and back surfaces, a structuretermed an “inner rib” is employed. Thus, the first wall and the secondwall are projected, in blow molding, until a part of the second wallcontacts with a wall to be linked integrally within the hollow spacethere between.

The automobile industry uses hollow articles because of the mechanicalproperties and weight characteristics. Automotive parts include consolebox lid, hood, door panel, and air conditioning duct. For example, inorder to assure the rigidity as a product or to protect the crew fromimpact of collision, an automotive roof side duct is disposed near bothsides of ceiling as explained in Japanese Patent Application Laid-OpenNo. 2000-43541.

The automobile industry is particularly interested in increasing thesafety of the vehicles, and at a minimum, complying with the certainsafety guidelines. According to the Federal Motor Vehicle SafetyStandards (FMVSS), the hollow articles must have a minimum level ofimpact absorption. The guidelines are established under the Departmentof Transportation by the National Highway Traffic Safety Administration.There are a number of guidelines and requirements, including FMVSS 201that addresses occupant protection in interior impact. There are otherguidelines that describe related topics such as resistance to roofcrushing. Head injuries are calculated according to a ‘heading injurycriteria’ (HIC) that is obtained from the deceleration of the headduring the duration of the impact. These federal standards must besatisfied in order for vehicle to enter the U.S. market. And, theseregulations are continuously being updated as new innovations andfeatures result in improved safety characteristics.

There are many studies that demonstrate that significant head injuriesand trauma occur when the driver or passengers head strikes the interiorroof and side panels. A rigid interior wall offers little impactabsorbing qualities when struck by a human head. There are a number oftechniques used to impart some shock absorbing qualities into the roofand interior panels, but the strict government standards continue toincrease and demand greater safety thresholds. The use of ceiling airbags and structural modifications to the support elements are designedto address the impact absorbing qualities, however there are issues suchas cost and manufacturability that limit the wide-spread use of suchfeatures.

As shown in prior art FIG. 11, the inner rib of a roof side duct isintegrally formed by blow molding, wherein an inside wall 101 facing aceiling interior member 107 and an outside wall 102 facing an innerpanel 106 of car body confront each other. A flat impact absorbing rib103 is disposed along the longitudinal direction in a space 110 betweenthe inside wall 101 and outside wall 102. A general manufacturing methodof this roof side duct is explained by referring to FIG. 12a, 12 b, andFIG. 13.

Prior art FIG. 12a shows a molten parison 300 being poured into openedsplit molds 201, 202, and then the molds are closed. Next, a rib formingplate 203 is projected toward the second mold 202, and a neck 303 isformed in the area of first wall 301 of the parison, and its leading endis pressed tightly to the area of second wall 302. Then, as shown inFIG. 12a, the rib forming plate 203 is pulled in, the pressurized air isintroduced into the parison 300, and is inflated into a shape along thecavity by the internal pressure of the pressurized air, and the neck 303is pressed and deformed in the direction of the arrows, whileconfronting walls are fused integrally, so that an impact absorbing rib304 is formed.

According to the prior art, as shown in FIG. 13, when pulling in the ribforming plate 203, after projecting the rib forming plate and forming aneck at first wall side of the parison, the neck is dragged in thebackward direction of the rib forming plate 203, or is elongated by theblow pressure in the blow process, and the wall thickness and width ofthe flat rib formed as the confronting walls of the neck are compressedfrom both sides by internal pressure of the pressurized air aredecreased. Thus, at portion 305 the inner rib is reduced in wall widthand the shape, and the dimensions and wall thickness of the flat rib arenot uniform on the whole. As a result, the rigidity and other mechanicalstrength of the impact absorbing rib 304 are lowered, and the ducthaving sufficient impact absorbing performance is lessened. Furthermore,the varying thickness of the inner rib results in some inconsistency inimpact absorbing qualities. In the described application, such a productmay result in inadequate protection in the event of a collision. Otherapplications may result in improper rigidity and strength and at thevery least, inconsistency in the produced hollow article.

What is needed is a hollow article with a rib of uniform shape,dimensions and wall width. The rib should have excellent mechanicalstrength and properties. In one embodiment, such as automotive, thehollow article with the rib should have impact absorbing qualities toprotect the driver and passengers. The manufacturing method for such animproved hollow article should be cost-effective and have a low defectrate.

SUMMARY OF THE INVENTION

The invention is devised in the light of the problems of the prior artdescribed herein. The present invention is a hollow article having animpact absorbing rib uniform in shape, dimensions and wall width on thewhole, especially free from reduction of wall width of the inner rib,yet possessing proper rigidity and mechanical strength, and excellentimpact absorbing performance.

Another aspect of the invention is to ensure compliance with the FMVSS201 regulations addressing interior head injury criteria. According toFMVSS 201, the interior of the vehicle in the U.S marketplace must havea head injury criteria (HIC) of less than 1000. The value is determinedby striking a dummy head of a certain mass into the regions of thevehicle interior at a certain speed and measuring the shock value. Thepresent invention results in an article that is well within the federalguidelines. In addition, present invention has a greater consistency andrepeatability as compared to prior art products that have a higher rateof failure of compliance. The prior art components are generally unableto satisfy the HIC standards, and therefore cannot pass the FMVSS 201specifications. For example, the roof side ducts of the prior art weretested and the HIC was found to be approximately 1500, which is abovethe 1000 HIC threshold.

One object of the invention is a hollow article made of a thermoplasticresin and integrally formed by blow molding, comprising a first wall anda second wall confronting across a spacing, an integral rib between thefirst wall and the second wall, wherein the integral rib comprises aflat rib projecting from the second wall to the first wall, and a hollowrib adjacent to each of two side ends of the flat rib, wherein the flatrib and the hollow rib are fused to an inner side of the first wall.

A further object is the hollow article, wherein the hollow rib istapered with a more narrow portion at the first wall. Additionally,wherein the integral rib is disposed along a longitudinal direction ofthe hollow article. And, wherein a plurality of the integral ribs aredisposed at a mutual spacing.

An additional object is the hollow article, wherein the integral rib isdisposed in an impact action direction. Also, wherein the hollow articleis an automobile component

An object of the invention is a hollow article made of thermoplasticresin, integrally formed by blow molding, comprising a first wall and asecond wall confronting across a spacing, an integral rib disposedbetween the first wall and the second wall, wherein the integral ribcomprises a first flat rib projecting from the first wall to a fusionportion, a first hollow rib adjacent to each of two side ends of thefirst flat rib, a second flat rib projecting from the second wall to thefusion portion, a second hollow rib adjacent to each of two side ends ofthe second flat rib, wherein the first flat rib and the second flat ribare fused to each other at the fusion portion, and wherein the firsthollow rib and the second hollow rib are fused to each other at thefusion portion.

Another object is the hollow article, wherein the first hollow rib andthe second hollow rib form a combined concave hollow rib. Also, thehollow article, wherein the integral rib is disposed along alongitudinal direction of the hollow article. Additional objects of theinvention include the hollow article, wherein a plurality of theintegral ribs are disposed at a mutual spacing, and also wherein theintegral rib is disposed in an impact action direction.

An object of the invention is a method of blow molding a hollow articlehaving a first wall and a second wall confronting across a spacing, withan integral rib disposed between the first wall and the second wall,comprising the steps of opening a split mold, wherein the split mold hasa first mold half with a cavity, a slide core and a pair of supportcores on either side of the slide core, and a second mold half with acavity, a slide core and a pair of support cores on either side of theslide core. Extruding a parison of molten thermoplastic resin betweenthe split mold and closing the split mold, thereby deforming the parisonwith each sliding core and each of the pair of support cores and forminga first recess and a second recess, wherein a leading end of the firstrecess and a leading end of the second recess are fused. Next,retracting each of the slide cores and introducing a pressure substanceinto the parison and inflating the parison along a cavity surface of thesplit molds and the support cores and forming the integral rib betweenthe first wall and the second wall, wherein the integral rib comprises apair of flat ribs and a pair of hollow ribs, and cooling the split mold,opening the split mold and removing the hollow article.

And additional object is the method of blow molding, wherein the step ofretracting the slide cores is simultaneous with the step of introducingthe pressure substance. Also, wherein the pressurized substance is agas.

An object of the invention is a method of blow molding a hollow articlehaving a first wall and a second wall confronting across a spacing, withan integral rib disposed between the first wall and the second wall,comprising the steps of opening a split mold, wherein the split mold hasa first mold half with a cavity, and a second mold half with a cavity, aslide core and a pair of support cores on either side of the slide core,extruding a parison of molten thermoplastic resin between the splitmold, closing the split mold, deforming the parison with the slidingcore and the pair of support cores and forming a recess, wherein aleading end of the recess is fused to an inner surface of an opposingwall side. Finally, retracting the slide core, introducing a pressuresubstance into the parison, inflating the parison along a cavity surfaceof the split molds and the support cores and forming the integral ribbetween the first wall and the second wall, wherein the integral ribcomprises a flat rib and a pair of hollow ribs, cooling the split mold,opening the split mold and removing the hollow article.

A further object is the blow molding method, wherein the step ofretracting the slide cores is simultaneous with the step of introducingthe pressure substance. Furthermore, wherein the pressurized substanceis a gas.

An object of the invention is an apparatus for blow molding a hollowarticle from a thermoplastic resin, having a first wall and a secondwall confronting across a hollow space, and an integral rib disposed forproviding structural support and absorbing impact between the first walland the second wall, comprising a split mold with a first mold half anda second mold half, a slidably engageable slide core for forming a flatrib disposed in at least one of the mold halves, a pair of support coresdisposed on at least one of the mold halves for forming a hollow rib andadjacent to each of two side ends of the slide core, and a means ofretracting the sliding core.

Additionally, the apparatus for blow molding, wherein the pair ofsupport cores is integrally disposed in the mold halves. And, whereinthe pair of support cores is retractable from within the mold halves.Finally, the apparatus for blow molding wherein a surface of the slidecore is treated with fluorine film coating so as to slide smoothly withthe parison.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein I have shown and described only apreferred embodiment of the invention, simply by way of illustration ofthe best mode contemplated by me on carrying out my invention. As willbe realized, the invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings,wherein like reference numerals designate like structural elements, andin which:

FIG. 1a shows a hollow article for an automobile according to a firstembodiment of the invention, in which A is a schematic partialperspective view broken in the portion of impact absorbing rib

FIG. 1b shows a hollow article for an automobile according to a firstembodiment of the invention showing a schematic partial sectional viewalong line A—A in FIG. 1a

FIG. 2a shows a hollow article for an automobile according to a secondembodiment of the invention, showing a schematic partial perspectiveview broken in the portion of impact absorbing rib

FIG. 2b shows a hollow article for an automobile according to a secondembodiment of the invention, showing a schematic partial sectional viewalong line A—A in FIG. 2a

FIG. 3 is an explanatory diagram showing an example of use of the hollowarticle for an automobile

FIG. 4a is an example of a manufacturing method of the hollow articlefor an automobile, with an explanatory diagram showing a state ofdisposing a parison between opened molds

FIG. 4b is an example of a manufacturing method for the hollow articlefor an automobile, showing a schematic sectional view along line A—A inFIG. 4a.

FIG. 5a shows a completely closed state of the molds after the processshown in FIG. 4a, illustrating a schematic partial sectional view alongthe axial direction of parison

FIG. 5b shows a completely closed state of the molds after the processshown in FIG. 4a, illustrating a schematic sectional view along line A—Ain FIG. 5a

FIG. 6a shows a completely withdrawn state of the slide core after theprocess shown in FIG. 5a, depicting a schematic partial sectional viewalong the axial direction of parison

FIG. 6b shows a completely withdrawn state of the slide core after theprocess shown in FIG. 5a, depicting a schematic sectional view alongline A—A in FIG. 6a

FIG. 7a shows a completely introduced state of the pressurized air afterthe process shown in FIG. 6a, showing a schematic partial sectional viewalong the axial direction of parison

FIG. 7b shows a completely introduced state of the pressurized air afterthe process shown in FIG. 6a, showing a schematic sectional view alongline A—A in FIG. 7a

FIG. 8a is another example of a manufacturing method of a hollow articlefor the automobile, depicting an explanatory diagram showing a state ofdisposing a parison between opened molds

FIG. 8b is another example of a manufacturing method of a hollow articlefor the automobile, depicting a schematic sectional view along line A—Ain FIG. 8a.

FIG. 9a shows a completely closed state of the molds after the processshown in FIG. 8a, illustrating a schematic partial sectional view alongthe axial direction of parison

FIG. 9b shows a completely closed state of the molds after the processshown in FIG. 8a, illustrating a schematic sectional view along line A—Ain FIG. 9a

FIG. 10a shows a completely introduced state of the pressurized airafter the process shown in FIG. 9a, showing a schematic partialsectional view along the axial direction of parison

FIG. 10b shows a completely introduced state of the pressurized airafter the process shown in FIG. 9a, showing a schematic sectional viewalong line A—A

FIG. 11 is a prior art schematic sectional view after installation of aninner panel, showing a conventional roof side duct.

FIG. 12a is a prior art process for manufacturing the roof side ductshown in FIG. 11, depicting a schematic sectional view showing a formingstate with the narrow neck in the parison by the rib forming plate

FIG. 12b is a prior art process for manufacturing the roof side ductshown in FIG. 11a, depicting a schematic sectional view showing a stateupon completion of the introduction of pressurized air

FIG. 13 is a prior art schematic sectional view along line X—X in FIG.12b

FIG. 14 is a sectional view side view showing shape of the hollow ribfor the embodiment using two sliding cores, wherein the combined hollowribs are concave in appearance

FIG. 15 is a sectional view side view shape of the hollow rib for theembodiment using one sliding core, wherein the hollow rib is tapered inappearance

REFERENCE NUMERALS

FIGS. 1a, 1 b, 14

1 Hollow matter for automobile

2 First wall

3 Second wall

4 First side wall

5 Second side wall

6 First flat rib

7 Second flat rib

8 First hollow rib

9 Second hollow rib

10 Impact absorbing rib

11 Fusion portion

FIGS. 2a, 2 b, 15

21 Hollow matter for automobile

22 First wall

23 Second wall

26 Flat rib

27 Hollow rib

30 Impact absorbing rib

31 Fusion portion

FIG. 3

2 First wall

3 Second wall

4 First side wall

5 Second side wall

35 Connection duct

35 a, 35 b Junction

36 Discharge port

FIGS. 4a, 4 b

41 First mold

41 a, 42 b Cavity

42 Second mold

43 Extrusion head

44 Parison

45, 47 Slide core

46, 48 Support core

FIGS. 5a, 5 b

44 a First recess

44 b Second recess

51 Fusion portion

FIG. 6

44 Parison

FIGS. 7a, 7 b

1 Hollow matter for automobile

2 First wall

3 Second wall

6 First flat rib

7 Second flat rib

8 First hollow rib

9 Second hollow rib

51 Fusion portion

FIGS. 8a, 8 b

61 First mold

62 Second mold

63 Extrusion head

64 Parison

65 Slide core

FIGS. 9a, 9 b

64 Parison

64 a Recess

65 Slide core

66 Support core

71 Fusion portion

FIGS. 10a, 10 b

22 First wall

23 Second wall

24 First side wall

25 Second side wall

26 Flat rib

31 Fusion portion

61 First mold

61 a Cavity

62 Second mold

65 Slide core

66 Support core

FIG. 11

101 Inside wall

102 Outside wall

103 Impact absorbing rib

106 Inner panel

107 Ceiling interior member

110 Space

FIGS. 12a, 12 b

201 Split mold

202 Split mold

203 Rib forming plate

300 Parison

301 Support core

302 Second wall

303 Neck

304 Impact absorbing rib

FIG. 13

304 Impact absorbing rib

305 Reduced portion

DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of the hollow article of the present invention,typically used in the automobile industry, is described in detailherein. FIG. 1a shows the hollow article as a partial perspective viewbroken in the portion of impact absorbing rib. FIG. 1b is a partialsectional view along line A—A in FIG. 1a.

The hollow article 1 of FIG. 1a is made of thermoplastic resin that isintegrally formed by blow molding. It includes a first wall 2 and asecond wall 3 mutually confronting across a space in an impact actingdirection. The impact absorbing direction refers to the orientation ofthe hollow article in the desired application. For example, if thehollow article 1 were deployed in a roof of an automobile, either thefirst or second wall 2, 3 would be facing the interior of the vehicleand subject to being struck by the head of driver and/or passengers.

In this particular described embodiment the first wall 2 and second wall3 are inclined with respect to each other. There is a first side wall 4and a second side wall 5 formed consecutively to both side ends of thefirst wall 2 and second wall 3 confronting nearly parallel to eachother.

The sectional shape of the hollow article 1 is not limited to thetrapezoidal shape as shown in the embodiment of FIG. 1a with respect tothe mutually confronting first wall 2 and second wall 3 being inclined.The article 1 may be formed as a square, rectangle, parallelogram orother arbitrary shape depending on the application and still be withinthe scope of the present invention.

Between the first wall 2 and second wall 3, there is an impact absorbingrib 10 formed integrally by blow molding. This impact absorbing rib 10includes a first flat rib 6 projecting from the first wall 2 with afirst hollow rib 8 adjacent to both side ends of the first flat rib 6. Asecond flat rib 7 projects from the second wall 3 with a second hollowrib 9 adjacent to both side ends of the second flat rib 7. The first andsecond flat rib 6, 7 meet at the fusion portion 11 as do the first andsecond hollow rib 8, 9. In a preferred embodiment the flat rib 6, 7 isgenerally rectangular with side ends connected to the hollow ribs 8, 9.

In the embodiment shown in FIG. 14, the shape of the interconnectedfirst and second hollow ribs 8, 9 is concave. The concave appearance isa result of the mating of the first hollow rib 8 and the second hollowrib 9 at the fusion portion 11. The first hollow rib 8 and second hollowrib 9 are both tapered such that they are more narrow at the fusionportion 11, resulting in a concave structure in one embodiment of theinvention. The tapered appearance of the first and second hollow rib 8,9 is affected by the shape of the support core to some extent. Thus, inone of the embodiments, a tapered support core with a narrow portionextending to the fusion portion affects the shape of the hollow rib.However, the present invention is not limited to a concave shape for thehollow rib 8, 9.

A second embodiment of a hollow article 21, also useful in theautomobile industry is described and depicted in FIGS. 2a and 2 b. FIG.2a shows a hollow article 21 according to the second embodiment, aschematic partial perspective view broken in the portion of impactabsorbing rib. FIG. 2b is a schematic partial sectional view along lineA—A in FIG. 2a.

A hollow article 21 is made of thermoplastic resin formed integrally byblow molding, and includes first wall 22 and second wall 23 mutuallyconfronting across a space in an impact acting direction. The secondwall 23 is inclined to the first wall 22 in this embodiment. A firstsidewall 24 and second sidewall 25 are formed consecutively to both sideends of the first wall 22 and second wall 23 respectively and confrontnearly parallel to each other.

Between the first wall 22 and second wall 23, there is an impactabsorbing rib 30 formed integrally by blow molding. This impactabsorbing rib 30 includes a flat rib 26 projecting from second wall 23to first wall 22 and a hollow rib 27 adjacent to both side ends of theflat rib 26 which are integrated through a fusion portion 31.

As shown in FIG. 15, the shape of the impact absorbing rib 30 istapered. The tapered appearance is a result of the mating of the hollowrib 27 to the fusion portion 31. The hollow rib 27 is both tapered suchthat it is more narrow at the fusion portion 31. However, the presentinvention is not limited to a tapered shape for the impact absorbing rib30.

The thermoplastic resin used for blow molding the hollow article is notparticularly limited, and any of the thermoplastic grade materials areacceptable. Various compounds may be used for the present invention, andpreferred examples include high-density polyethylene, medium densitypolyethylene, polypropylene, denatured polyphenylene oxide,polycarbonate, polyamide, and ABS resin.

The hollow article of the present invention may be used in automobileapplications, such as for automobile damper, hood, door, console boxlid, air conditioning duct, and other interior and exterior parts. Theimplementation of the present invention in the automotive industry canenhance the safety of the vehicle and provide better protection for thedriver and passengers.

The head injury criteria obtained by the present invention wasapproximately 800, which is within the guidelines established by FMVSS201. Prior art hollow articles tested had a head injury criteria thatwas above the limit set by FMVSS 201. In addition, one of the advantagesof the present invention is the repeatability, reliability andconsistency of the hollow articles. Prior art articles tend to have amuch greater variability in the thickness and dimensions of the impactabsorbing rib and effecting the head injury criteria.

FIG. 3 illustrates an example of the hollow article shown in FIG. 1a inthe air conditioning duct for an automobile, disposed at both sides ofthe car compartment ceiling. As shown in FIG. 3, the hollow article 1 isdisposed at both sides of the car compartment ceiling and shows twoimpact absorbing ribs 10 disposed at an interval along the longitudinaldirection of the compartment ceiling ducts. One end of the ductsinterconnect with junctions 35 a, 35 b which are disposed at both sidesof a connection duct 35 and the second end side of the duct is closed.First wall 2 and second side wall 5 face the inside of the compartment,and second wall 3 and first side wall 4 face the car body side, and adischarge port 36 is provided at a position not forming the impactabsorbing rib 10 of first wall 2.

The air conditioning air supplied from the air conditioner (not shown)through the connection duct 35 is discharged toward the passengers anddriver through a passage of the hollow article 1 formed at both sides ofthe impact absorbing rib 10, from the discharge port 36, so that thecompartment can be air conditioned uniformly.

In the event of a car crash, if the head of a driver or passengercollides against the first wall 2, this impact is absorbed by the impactabsorbing rib 10 lessening the effects or damages from the impact.

The impact absorbing rib 10 as described herein is not limited to asingle rib per article. As shown in FIG. 3, two or more impact absorbingribs 10 may be disposed as required at a mutual spacing. Thedetermination of the mutual spacing depends upon many factors includingthe required structural support, length of the article, dimension of thearticle, compounds used to manufacture the article, as well the intendedimpact absorbing qualities desired.

An example of a manufacturing system of the hollow article is explainedin detail in FIGS. 4a and 4 b. This particular embodiment utilizes twosliding cores 45, 47. A first mold 41 and second mold 42 are opened. Inone embodiment the support cores 46, 48 and slide cores 45, 47 areprojecting to a position where the leading ends 45 a, 47 a of thesliding cores are nearly flush with leading ends 46 a, 48 a of thesupport cores 46, 48, and wherein the sliding core is a generallyrectangular flat plate disposed between the support cores.

The first mold 41 includes a cavity 41 a for defining the outer surfaceof nearly half of the first wall 2 side of tie hollow article, the slidecore 45 for forming first flat rib 6, and a pair of support cores 46 forforming first hollow rib 8 disposed adjacently to both side ends offirst flat rib 6. By contrast, the second mold 42 includes a cavity 42 afor defining the outer surface of the remaining portion of the secondwall 3 side of the hollow article, the slide core 47 for forming secondflat rib 7, and a pair of support cores 48 for forming second hollow rib9 disposed adjacently to both side ends of second flat rib 7.

The support cores 46, 48 are not limited to the illustrated example.Retractable support cores 66 like those shown in FIG. 8 may be also usedin the present invention.

Next, a parison 44 made of molten thermoplastic resin is extruded froman extrusion head 43 of an extruder (not shown) and is poured into theopened molds 41, 42, and then the molds 41, 42 are gradually closed.

As the molds 41, 42 are being closed, with or without a time delay, theslide core 45 and support cores 46 of the first mold project towards theslide core 47 and support cores 48 of the second mold 42. As the moldsare being closed, as shown in FIGS. 5a and 5 b, the first wall side ofthe parison 44 is pushed and deformed by the slide core 45 and supportcores 46 of the first mold 41 and one recess 44 a is formed, while thesecond wall side of the parison 44 is pushed and deformed by the slidecore 47 and support cores 48 of the second mold 42 and second recess 44b is formed. When the molds 41, 42 are completely closed, the leadingend of first recess 44 a and leading end of second recess 44 b arefused, and a fusion portion 51 is formed.

Then the slide cores 45, 47 are retracted as shown in FIGS. 6a and 6 b.In this case, both sides of first recess 44 a and second recess 44 b arefixed at their positions by the support cores 46, 48. Only slide cores45, 47 are drawn back, and therefore as the slide cores 45, 47 areretracted, the recesses 44 a, 44 b formed in the parison 44 are notdragged. The combination of the elements contribute to the hollow ribbeing formed about the support cores with uniform and consistentstructural dimensions. Contributing to the production is the surfacetension of the thermoplastic material at the fusion portion to maintainthe shape within the molds 41, 42 while the sliding cores 45, 47 areretracted.

An inflation or blow means such as a blow needle (not shown) is pokedinto the parison 44, and pressurized air is introduced to inflate theparison 44 into a shape along the outer surface of the cavities 41 a, 42a and support cores 46, 48, and the wall surfaces facing the recesses 44a, 44 b are pressed and deformed by internal pressure of the pressurizedair, as shown in FIGS. 7a and 7 b. Although pressurized air is used inthis embodiment, it is also within the scope of the invention to utilizepressurized gases to inflate the parison 44.

As a result of the pressurized air, the first wall 2 and second wall 3are disposed in a confronting orientation. Between the first wall 2 andsecond wall 3, the leading ends of the first flat rib 6 project from thefirst wall 2. The first hollow rib 8, adjacent to both side ends offirst flat rib 6, projects from the first wall 2. The leading ends ofthe second flat rib 7 project from second wall 3. The second hollow rib9, adjacent to both side ends of second flat rib 7, projects from thesecond wall 3. The first flat rib 6 and second flat rib 7 are integratedthrough the fusion portion 11, thereby completing impact absorbing rib10.

After cooling in the molds 41, 42, and opening the molds, the hollowarticle 1 is removed and deflashed.

Another example of a manufacturing method of the hollow article of thepresent invention is explained herein. As shown in FIGS. 8a, 8 b, firstmold 61 and second mold 62 are opened with the slide core 65 and supportcore 66 of the first mold 61 and second mold 62 retracted as shown.

Herein, the first mold 61 includes a cavity 61 a for defining the outersurface of nearly half of the first wall 22 side of the hollow article21. By contrast, the second mold 62 includes a cavity 62 a for definingthe outer surface of the remaining portion of the second wall 23 side ofthe hollow article 21, the slide core 65 for forming a flat rib 26, anda pair of support cores 66 for forming a pair of hollow ribs 27 disposedadjacently to both side ends of the flat rib 26. In this particularembodiment the pair of support cores 66 are retractable. The supportcores 66 are not limited to the illustrated retractable example, but maybe disposed integrally in the second mold 62.

A parison 64 made of molten thermoplastic resin is extruded from anextrusion head 63 of an extruder not shown in the diagram, and is pouredinto the opened molds 61, 62, and the molds are closed.

As the molds 61, 62 are being closed, with or without a time delay, theslide core 65 and support core 66 project toward the second mold 66, asshown in FIGS. 9a and 9 b. The first wall side of the parison 64 ispushed and deformed and a recess 64 a is formed, then the leading end ofthe recess 64 a is fused to the inner surface of the second wall side ofthe parison, and a fusion portion 71 is formed.

After closing the molds 61, 62, while the support core 66 is projecting,the slide core 65 is retracted. As the slide core 65 is retracted, therecess 64 a formed in the parison 64 is not dragged or otherwisedeformed.

Next, blow means, such as a blow needle (not shown), is poked into theparison 64, and pressurized air is introduced to inflate the parison 64,as shown in FIGS. 10a and 10 b into a shape along the outer surface ofthe cavities 61 a, 62 a and support core 66. The wall surface facing therecess 64 a is pressed and deformed by internal pressure of thepressurized air. Other means of introducing pressurization are wellknown in the art and are within the scope of the present invention.

As defined herein, the term gas includes air, other gases, and anycombination of gases and air. The use of such gases for pressurizationis known in the art, the present invention is not limited to air. Othergases are well within the scope of the invention such as nitrogen gas.

As a result, the confronting first wall 62 and second wall 63 aredisposed at an interval to provide proper rigidity and impact absorbingqualities. The ribs are orientated in the impact action directionbetween the first wall 62 and second wall 63. The leading ends of theflat rib 26 projecting from first wall 62 to second wall 63 and thehollow rib 27 adjacent to both side ends of the flat rib 26 areintegrated through the fusion portion 71 on the inner surface fromsecond wall 63, thereby completing the impact absorbing rib 30.

The final step involves cooling in the molds, opening the molds 61, 62,removing the hollow article 21, and deflashing. The support cores, ifretractable, can be retracted once the hollow ribs are formed.

In the manufacturing method of the hollow article according to theinvention, the surface of the slide core retractably disposed in themold may be covered with a coating layer made of fluoroplastic resinwhich makes it easier to slide. The application of the coating layer offluoroplastic resin is improved by roughening the surface of the slidecore and then applying a coating layer of fluoroplastic resin on therough surface.

The coating layer is not limited to a thin layer of fluoroplastic resin,but can also be formed by co-deposition of fluoroplastic resin andplating solution such as electroless nickel in a treating solution, andapplying and baking the treating solution on the surface of the slidecore. Alternatively, the coating layer can also be prepared by formingan electroless nickel coating on the surface of the slide core, andimpregnating fluoroplastic resin in this electroless nickel coating.

The hollow article of the present invention, used for example in theautomotive industry, encompasses an impact absorbing rib made of flatrib and hollow rib disposed adjacently to both side ends of the flat riband is integrally formed between the confronting first wall and secondwall disposed at an interval in impact action direction. There is animpact absorbing rib uniform in shape, dimensions and wall thickness onthe whole and is integrally formed by blow molding. As a result, ahollow article useful with an excellent impact absorbing performance isobtained.

The objects and advantages of the invention may be further realized andattained by means of the instrumentalities and combinations particularlypointed out in the appended claims. Accordingly, the drawing anddescription are to be regarded as illustrative in nature, and not asrestrictive.

What is claimed is:
 1. A method of blow molding a hollow article havinga first wall and a second wall confronting across a spacing, with anintegral rib disposed between said first wall and said second wall,comprising the steps of: opening a split mold, wherein said split moldhas a first mold half with a cavity, and a second mold half with acavity, a slide core and a pair of support cores on either side of saidslide core; extruding a parison of molten thermoplastic resin betweensaid split mold; closing said split mold; deforming said parison withsaid sliding core and said pair of support cores and forming a recess,wherein a leading end of said recess is fused to an inner surface of anopposing wall side; retracting said slide core; introducing a pressuresubstance into said parison; inflating said parison along a cavitysurface of said split molds and said support cores and forming saidintegral rib between said first wall and said second wall, wherein saidintegral rib comprises a flat rib and a pair of hollow ribs; and coolingsaid split mold, opening said split mold and removing said hollowarticle.
 2. The method of blow molding a hollow article according toclaim 1, wherein said step of retracting said slide cores issimultaneous with said step of introducing said pressure substance. 3.The method of blow molding a hollow article according to claim 1,wherein said support cores are retractable.
 4. The method of blowmolding a hollow article according to claim 1, further comprising thestep of retracting said support cores after said article has cooled. 5.The method of blow molding a hollow article according to claim 1,wherein said pressurized substance is a gas.
 6. The method of blowmolding a hollow article according to claim 5, wherein said gas ischosen from the group of gasses consisting of nitrogen and air.
 7. Themethod of blow molding a hollow article according to claim 1, furthercomprising, before the step of extruding a parison, the steps of:roughening a surface of said slide core; and coating said surface ofsaid slide core with fluoroplastic resin.
 8. The method of blow moldinga hollow article according to claim 1, further comprising, after thestep of extruding a parison, the step of: maintaining the mold in anopen position.
 9. A method of blow molding a hollow article having afirst wall and a second wall confronting across a spacing, with anintegral rib disposed between said first wall and said second wall,comprising the steps of: opening a split mold, wherein said split moldhas a first mold half with a cavity, a slide core and a pair of supportcores on either side of said slide core, and a second mold half with acavity, a slide core and a pair of support cores on either side of saidslide core; extruding a parison of molten thermoplastic resin betweensaid split mold; closing said split mold; deforming said parison witheach said sliding core and each of said pair of support cores andforming a first recess and a second recess, wherein a leading end ofsaid first recess and a leading end of said second recess are fused;retracting each of said slide cores; introducing a pressure substanceinto said parison; inflating said parison along a cavity surface of saidsplit molds and said support cores and forming said integral rib betweensaid first wall and said second wall, wherein said integral ribcomprises a pair of flat ribs and a pair of hollow ribs; and coolingsaid split mold, opening said split mold and removing said hollowarticle.
 10. The method of blow molding a hollow article according toclaim 9, wherein said step of retracting said slide cores issimultaneous with said step of introducing said pressure substance. 11.The method of blow molding a hollow article according to claim 9,wherein said support cores are retractable.
 12. The method of blowmolding a hollow article according to claim 9, further comprising thestep of retracting said support cores after said article has cooled. 13.The method of blow molding a hollow article according to claim 9,wherein said pressurized substance is a gas.
 14. The method of blowmolding a hollow article according to claim 13, wherein said gas ischosen from the group of gasses consisting of nitrogen and air.
 15. Themethod of blow molding a hollow article according to claim 9, furthercomprising, before the step of extruding a parison, the steps of:roughening a surface of said slide core; and coating said surface ofsaid slide core with fluoroplastic resin.
 16. The method of blow moldinga hollow article according to claim 9, further comprising, after thestep of extruding a parison, the step of: maintaining the mold in anopen position.